The present invention relates to electrical wire connectors; and more particularly, to twist-on type connectors such as those having a tapered coil of electrically conductive material within an insulating shell.
The ends of two or more wires for an electrical circuit are often connected together using a twist-on type wire connector. These connectors are available in a variety of sizes and shapes and commonly have a conical shaped body of insulating material, such as plastic, with an opening at the larger end. The opening communicates with a similarly tapered aperture which may have helical threads cut therein. The fastening operation is performed by inserting the stripped ends of two or more wires into the open end and rotating the connector so that the threads screw onto and twist the wires to form an electrical coupling. In an improvement of the basic connector a tapered coiled metal spring is inserted into the aperture of the insulating shell. The spring engages the bare wires and aids in providing a conductive path therebetween.
Twist-on type wire connectors frequently are used by electricians to connect two or more wires in a junction box within a building. Electricians typically twist the connectors on by hand, although hand tools such as a hexagonal socket wrench or nut driver sometimes are used. These connectors also are employed to make similar electrical couplings in a variety of electrical appliances. For example, connections between the wires of a ballast in a fluorescent lighting fixture and wires for the lamp sockets are made in this manner. In a factory, the wire connectors often are applied using an electrically or pneumatically powered nut driver, because of the high volume assembly at a fixed location. These power tools had a socket specifically designed to engage the body of the connector.
One of the difficulties is that the tool can easily apply an excessive amount of torque to the connector that is significantly greater than the predefined level established by the Underwriters Laboratory for making an optimum electrical connection. Although previous wire connectors of this type were designed to be as strong as possible the excessive torque often caused the connector to fracture in an uncontrolled, random manner. If such cracks went undetected, a short circuit could occur at the connection. In other cases the excessive torque fractured the producing either an open circuit or a high resistance path which over heated.
One solution to this problem was to use a torque limiting device between the driving element of the tool and the socket. However, torque limiting devices add additional expense to the tool, and require adjustment to the optimum level for each specific wiring application.